No (412)
Yes (18)
Number of found documents:
430
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Geometric resonances in reflectivity spectra of lead zirconate
Dočekalová, Zuzana; Hlinka, Jiří
2016 - English
The paper deals with effects of domain boundaries on the THz–frequency range dispersion of the complex dielectric permitivity tensor of lead zirconate. In the case of a sufficiently narrow domain widths (in comparison to the wave–length of the light used in the experiment), the effective–medium average permittivity shows additional peaks identified as geometric resonances, i.e. extraneous excitations created by thematerial interface. Features of the far–infrared reflectivity spectra of the twinned lead zirconate crystal in the limit of narrow and wide domains are estimated with the\nhelp of the damped harmonic oscillator model with paramaters fully determined fromrecent experiments.
Keywords:
geometric resonances; lead zirconate; antiferroelectrics; reflectivity; phonon
Available at various institutes of the ASCR
Geometric resonances in reflectivity spectra of lead zirconate
The paper deals with effects of domain boundaries on the THz–frequency range dispersion of the complex dielectric permitivity tensor of lead zirconate. In the case of a sufficiently narrow domain ...
Book of Abstracts of the 26th Joint Seminar Development of Materials Science in Research and Education
Kožíšek, Zdeněk; Král, Robert; Zemenová, Petra
2016 - English
Topics:\n- Trends in development of materials research\n- Education of materials science at the universities\n- Information about the research programmes of individual institutions\n- Information on equipment for preparation and characterisation of materials\n- Results of materials science research
Keywords:
material sciences
Available at various institutes of the ASCR
Book of Abstracts of the 26th Joint Seminar Development of Materials Science in Research and Education
Topics:\n- Trends in development of materials research\n- Education of materials science at the universities\n- Information about the research programmes of individual institutions\n- Information on ...
Cryogenic cooling system Brayton for 10 J/10 Hz Yb:YAG multi-slab based laser system at ELI-Beamlines project
Schustr, P.; Fibrich, Martin; Polan, Jiří; Rus, Bedřich; Dostálová, M.; Valdislav, P.; Simek, J.
2016 - English
We present design and operational prototype of cryogenic cooling system based on Bryton's cycle for 10J/10Hz Yb:YAG multi-slab laser system at ELI-Beamlines project.
Keywords:
Brayton; cryogenics; laser; cooling; ytterbium; design; prototype
Available at various institutes of the ASCR
Cryogenic cooling system Brayton for 10 J/10 Hz Yb:YAG multi-slab based laser system at ELI-Beamlines project
We present design and operational prototype of cryogenic cooling system based on Bryton's cycle for 10J/10Hz Yb:YAG multi-slab laser system at ELI-Beamlines project.
Microscopic characterization of graphene material and electronic quality across neighbouring, differently oriented copper grains
Čermák, Jan; Yamada, T.; Ganzerová, Kristína; Rezek, Bohuslav
2015 - English
We study graphene grown across the boundary of three such grains having bright, medium, and dark color in reflection. Raman micro-spectroscopy proves presence of mostly a monoor bi-layer graphene on all the grains. Yet intensity of Raman 2D band is grain-dependent: highest at the darkest grain and lowest at the brightest one. Contrary, conductive atomic force microscopy detects the highest conductivity at the brightest grain and the lowest current at the darkest grain. This is attributed to dominant electrical current path through graphene and underlying oxide thickness of which also depends on the type of copper grain. We correlate and discuss the results with view to better understanding of graphene growth and electronic properties on large area copper substrates.
Keywords:
graphene; chemical vapor deposition; atomic force microscopy; Raman spectroscopy; electronic properties
Available at various institutes of the ASCR
Microscopic characterization of graphene material and electronic quality across neighbouring, differently oriented copper grains
We study graphene grown across the boundary of three such grains having bright, medium, and dark color in reflection. Raman micro-spectroscopy proves presence of mostly a monoor bi-layer graphene on ...
Magnetic domains under mechanical stress in single crystal Ni-Mn-Ga
Kopecký, Vít; Heczko, Oleg
2015 - English
The complexity of Ni-Mn-Ga single crystal lies in combination of ferromagnetic domain structure and ferroelastic twinned microstructure. Magnetic domain structure for different twinned microstructure was studied using magneto-optical indicator film. Different orientations of magnetic domains can be observed at the same place of the sample thanks to magnetically induced structural reorientation by movement of twin boundaries. We investigated experimentally the changes of magnetic domain structure in the vicinity of mobile a/c twin boundary.
Keywords:
Ni-Mn-Ga; magnetic domains; twin boundary
Available at various institutes of the ASCR
Magnetic domains under mechanical stress in single crystal Ni-Mn-Ga
The complexity of Ni-Mn-Ga single crystal lies in combination of ferromagnetic domain structure and ferroelastic twinned microstructure. Magnetic domain structure for different twinned ...
Diamond coated AlGaN/GaN high electron mobility transistors - effect of deposition process on gate electrode
Vanko, G.; Ižák, Tibor; Babchenko, O.; Kromka, Alexander
2015 - English
We studied the influence of the diamond deposition on the degradation of Schottky gate electrodes (i.e. Ir or IrO2) and on the electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs). In present study, the diamond films were selectively deposited on the AlGaN/GaN circular HEMT by focused (ellispoidal cavity reactor) and linear antenna (surface wave) microwave plasma at different temperatures from 400°C to 1100°C. The preliminary results on electrical measurements on the diamond-coated c-HEMTs showed degraded electrical properties comparing to c-HEMTs before deposition process, which was attributed to degradation of the Ir gate electrodes even at temperatures as low as 400°C. On the other hand, metal oxide gate electrode layer (IrO2) can withstand diamond CVD process even at high temperatures (~900°C) which make it suitable for fabrication of all-in-diamond c-HEMT devices for high-power applications.
Keywords:
GaN HEMT; CVD diamond; iridium oxide; thermal stability; IV characteristics
Available at various institutes of the ASCR
Diamond coated AlGaN/GaN high electron mobility transistors - effect of deposition process on gate electrode
We studied the influence of the diamond deposition on the degradation of Schottky gate electrodes (i.e. Ir or IrO2) and on the electrical characteristics of AlGaN/GaN high electron mobility ...
Scanning thermal microscopy of thermoelectric pulsed laser deposited nanostructures
Vaniš, Jan; Zelinka, Jiří; Zeipl, Radek; Jelínek, Miroslav; Kocourek, Tomáš; Remsa, Jan; Navrátil, Jiří
2015 - English
New materials with high possible figure of merit ZT are of high interest as a promising candidates for thermoelectric applications such as energy harvesting. Miniaturization of such systems tends toward developing of the suitable characterization method with nanometer resolution ability. In our contribution, we present the development and experimental results of a simple scanning probe microscopy method for the relative thermal conductivity characterization. The possibility of the setup is demonstrated on the set of different thin thermoelectric layers grown from hot pressed targets by pulsed laser deposition on the reference Si substrate. All the measurements were performed on the commercial Veeco Multimode scanning AFM/STM microscope with home developed controller and by using PicoCal Inc. bolometer probes with tungsten resistive path. All the experiments were done in the air at the ambient condition. Additional sample treatment for the measurement will be also briefly described
Keywords:
Scanning thermal microscopy; figure of merit; thermoeletric materials
Available at various institutes of the ASCR
Scanning thermal microscopy of thermoelectric pulsed laser deposited nanostructures
New materials with high possible figure of merit ZT are of high interest as a promising candidates for thermoelectric applications such as energy harvesting. Miniaturization of such systems tends ...
Modeling of nanofibers interaction with the environment
Klicmanová, I.; Sveshnikov, Alexey
2015 - English
Nanomaterials change our life. Every day they find applications in new branches of technology. At the same time, some branches of technology, like civil engineering, are rather conservative and do not accept new approaches lightly. Nanotextiles exhibit a number of qualities that make them a promising material for civil engineering applications. They can potentially play a role of filters, protective layers, armature and others. Properties of the nanotextiles can be significantly influenced by parameters of technological process. Pure experimental search of the optimal technological parameters to achieve the desired properties of the final material can be very tedious. Thus, a theoretical dependence of the properties of the nanotextile on parameters of the technological process must be established. Two independent tasks must be solved for this: the dependence of nanotextile structure on technological parameters, and determination of physical, chemical or biological properties of a nanotextile of a given structure. In this paper we discuss steps necessary for the solution of the second task.
Keywords:
Van der Waals; DLVO potential; Monte Carlo simulations
Available at various institutes of the ASCR
Modeling of nanofibers interaction with the environment
Nanomaterials change our life. Every day they find applications in new branches of technology. At the same time, some branches of technology, like civil engineering, are rather conservative and do not ...
Study of photocatalytic activity of Zn.sub.x./sub.Cd.sub.1-x./sub.S quantum dots in dependence on their composition using methylene blue
Praus, P.; Svoboda, L.; Hospodková, Alice; Mamulová Kutláková, K.
2015 - English
ZnCdS quantum dots (QDs) with the different composition were prepared by precipitation of zinc and cadmium acetates with sodium sulphide in the presence of cetyltrimethylammonium bromide (CTAB) used for stabilization of their aqueous colloid dispersions. Transition energies of these quantum dots were determined from the UV-VIS spectra of QDs colloid dispersions and consequently used for calculation of the QDs sizes according to the Schrodinger equation. The ZnCdS QDs size was found to be significantly influenced by their composition: the QDs size decreased with the increasing Zn content. The photocatalytic activity of the ZnCdS QDs was studied using the methylene blue decomposition under UV irradiation. Different photocatalytic activity depending on the composition x was observed and explained. The maximal photocatalytic activity was achieved for x = 0.6 when the energy of the irradiation photons was still sufficient to generate electron-hole pairs in majority of the QDs and at the same time the photocatalytic surface area was maximal.\n
Keywords:
quantum dots; ZnCdS; photocatalysis; UV-VIS absorption; x-ray diffraction
Available at various institutes of the ASCR
Study of photocatalytic activity of Zn.sub.x./sub.Cd.sub.1-x./sub.S quantum dots in dependence on their composition using methylene blue
ZnCdS quantum dots (QDs) with the different composition were prepared by precipitation of zinc and cadmium acetates with sodium sulphide in the presence of cetyltrimethylammonium bromide (CTAB) used ...
AlSb/InAsSb/AlSb deep QWs for the two band high temperature superlinear luminescence
Hulicius, Eduard; Hospodková, Alice; Pangrác, Jiří; Mikhailova, M.
2015 - English
InAlAsSb/GaSb based hetero-nanostructures with deep quantum wells grown on GaSb are promising materials for the optoelectronic devices for near- and mid-IR spectral regions. Optical power and quantum efficiency of the LEDs based on the narrow bandgap semiconductor compounds (InGa)(AsSb) are limited by the nonradiative Auger recombination. Earlier we have proposed a method to increase the optical power in the bulk narrow bandgap and later in GaSb-based nanostructures with a deep QW by the effect of impact ionization on the QW with high band offset.
Keywords:
quantum wells; luminescence; AlSb/InAsSb/AlSb
Available at various institutes of the ASCR
AlSb/InAsSb/AlSb deep QWs for the two band high temperature superlinear luminescence
InAlAsSb/GaSb based hetero-nanostructures with deep quantum wells grown on GaSb are promising materials for the optoelectronic devices for near- and mid-IR spectral regions. Optical power and quantum ...
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